Question about SwitchBot Thermometer & Hygrometer

While searching to answer your question, I didn't find how many thermometers the app can handle. But I agree with NoisyKibbles that there are indications that the number of units is not limited. Your request (8 units) must be achievable in my opinion.

I've just bought 3 and was able to put all 3 in, but I couldn't find the information you asked for... I think you can put quite a few in, see what's noted on their site: There's no limit to the number of meters you can pair with a single mobile device. Users can connect several meters simultaneously to the same mobile phone. Similarly, a single meter can be paired with several mobile phones at the same time.